1. Field of the Invention
The present invention relates to an improvement in a toroidal type continuously variable transmission used as a transmission for a motor vehicle, for example, in order to realize a structure which can transmit great power and has sufficient endurance by adequetely supplying oil to a power transmitting portion needed.
2. Related Background Art
Application of a toroidal type continuously variable transmission as schematically shown in FIGS. 8 and 9 to a transmission of a motor vehicle has been investigated. For example, as disclosed in Japanese Utility Model Application Laid-Open No. 62-71465, in the toroidal type continuously variable transmission, an input side disc 2 is coaxially supported with an input shaft 1, and an output side disc 4 is secured to an end of an output shaft 3 coaxially disposed with the input shaft 1. Within a casing containing the toroidal type continuously variable transmission, trunnions 6, which rock around pivot shafts 5 located at positions twisted with respect to the input shaft 1 and the output shaft 3, are disposed between the input side disc 2 and the output side disc 4 in an axial direction.
That is to say, the trunnions 6 are provided at their outer surfaces with the pivot shafts 5, which are coaxial with each other. Further, proximal ends of displacement shafts 7 are supported on intermediate portions of the trunnions 6 so that inclination angles of the displacement shafts 7 can be adjusted by rocking the trunnions 6 around the pivot shafts 5. Power rollers 8 are rotatably supported around the displacement shafts 7 supported by the trunnions 6. The power rollers 8 are pinched between opposed inner surfaces 2a and 4a of the input and output side discs 2 and 4. Each of the inner surfaces 2a, 4a has, in section, a concave surface obtained by rotating an arc around the pivot shaft 5. Peripheral surfaces 8a of the power rollers 8 having spherical convex surfaces are contacted with the inner surfaces 2a, 4a. 
An urging device 9 of loading cam type is disposed between the input shaft 1 and the input side disc 2 so that the input side disc 2 can be elastically biased toward the output side disc 4 by the urging device 9. The urging device 9 comprises a cam plate 10 rotated together with the input shaft 1, and a plurality (for example, four) of rollers 12 rotatably held by a holder 11. A cam surface 13 made concave and convex alternately in a circumferential direction is formed on one side surface (right side surface in FIGS. 8 and 9) of the cam plate 10, and a cam surface 14 having a similar configuration is formed on an outer surface (left side surface in FIGS. 8 and 9) of the input side disc 2. The plurality of rollers 12 are supported for rotation around axes oriented radially with respect to the centerline of the input shaft 1.
In use of the toroidal type continuously variable transmission having the above-mentioned construction, when the cam plate 10 is rotated as the input shaft 1 is rotated, the cam surface 13 urges the plurality of rollers 12 against the cam surface 14 formed on the outer surface of the input side disc 2. As a result, the input side disc 2 is urged against the plurality of power rollers 8 and, at the same time, the input side disc 2 is rotated due to the urging between the cam surfaces 13, 14 and the plurality of rollers 12. The rotation of the input side disc 2 is transmitted to the output side disc 4 through the plurality of power rollers 8, thereby rotating the output shaft 3 secured to the output side disc 4.
In a case where a rotational speed ratio (transmission ratio) between the input shaft 1 and the output shaft 3 is changed, when deceleration (speed reduction) is effected between the input shaft 1 and the output shaft 3, the trunnions 6 are rocked in predetermined directions around the pivot shafts 5. And, the displacement shafts 7 are inclined so that, as shown in FIG. 8, the peripheral surfaces 8a of the power rollers 8 abut against a portion near the center of the inner surface 2a of the input side disc 2 and a portion near the peripheral of the inner surface 4a of the output side disc 4, respectively. On the other hand, when acceleration (speed increase) is effected, the trunnions 6 are rocked in opposite directions around the pivot shafts 5. And, the displacement shafts 7 are inclined so that, as shown in FIG. 9, the peripheral surfaces 8a of the power rollers 8 abut against a portion near the peripheral of the inner surface 2a of the input side disc 2 and a portion near the center of the inner surface 4a of the output side disc 4, respectively. When the inclination angles of the displacement shafts 7 are selected to an intermediate value between FIG. 8 and FIG. 9, an intermediate transmission ratio can be obtained between the input shaft 1 and the output shaft 3.
FIGS. 10 and 11 show an example of a more concrete toroidal type continuously variable transmission described in Japanese Utility Model Application Laid-Open No. 1-173552. An input side disc 2 and an output side disc 4 are rotatably supported around a cylindrical input shaft 15 via needle bearings 16. Further, a cam plate 10 is spline-connected to an outer peripheral surface of the input shaft 15 at an end thereof (left end in FIG. 10), and the cam plate is prevented from being shifted away from the input side disc 2 by means of a flange 17. The cam plate 10 and rollers 12 constitute an urging device 9 for rotating the input side disc 2 while urging it toward the output side disc 4 as the input shaft 15 is rotated. An output gear 18 is joined to the output side disc via keys 19 so that the output side disc 4 and the output gear 18 are rotated in a synchronous manner.
Pivot shafts 5 provided on both ends of a pair of trunnions 6 are supported by a pair of support plates 20 for rocking movement and axial displacement (in a direction perpendicular to the plane of FIG. 10 and a left-and-right direction in FIG. 11). Displacement shafts 7 are supported in circular holes 21 formed in intermediate portions of the trunnions 6. The displacement shafts 7 have parallel and eccentric support shaft portions 22, and pivot shaft portions 23. The support shaft portions 22 are rotatably supported in the circular holes 21 via radial needle bearings 24. Further, power rollers 8 are rotatably supported around the pivot shaft portions 23 via radial needle bearings 25.
Incidentally, the pair of displacement shafts 7 are disposed at positions diametrically opposed with respect to the input shaft 15. Further, directions along which the pivot shaft portions 23 of the displacement shafts 7 are eccentric with respect to the support shaft portions 22 are the same directions (opposite directions in FIG. 11) with respect to the rotational directions of the input and output side discs 2, 4. Further, the eccentric directions are substantially perpendicular to the installation direction of the input shaft 15. Accordingly, the power rollers 8 are supported for slight displacement in the axial direction (left-and-right direction in FIG. 10 and direction perpendicular to the plane of FIG. 11) of the input shaft 15. As a result, even if the power rollers 8 tend to be displaced in the axial direction of the input shaft 15 due to elastic deformation of the constructural parts caused by a great load acting on the constructural parts during the rotational force transmitting condition, such displacement can be absorbed without applying great or excessive force to the various parts.
Further, thrust ball bearings 26 and thrust needle bearings 27 are disposed between the outer surfaces of the power rollers 8 and the inner surfaces of the intermediate portions of the trunnions 6, and the thrust ball bearings 26 are located near the power rollers 8. The thrust ball bearings 26 serve to permit rotation of the power rollers 8 while supporting a thrust load acting on the power rollers 8. On the other hand, the thrust needle bearings 27 permit the pivot shaft portions 23 and outer races 28 of the thrust ball bearings 26 to be rocked around the support shaft portions 22 while supporting a thrust load acting on the outer races 28 from the power rollers 8.
Further, ends (left ends in FIG. 11) of the trunnions 6 are connected to drive rods 29, and drive pistons 30 are secured to outer peripheral surfaces of intermediate portions of the drive rods 29. The drive pistons 30 are mounted within drive cylinders 31 in an oil-tight manner.
In case of the toroidal type continuously variable transmission having the above-mentioned construction, the rotation of the input shaft 15 is transmitted to the input side disc 2 through the urging device 9. The rotation of the input side disc 2 is transmitted to the output side disc 4 through the pair of power rollers 8, and the rotation of the output side disc 4 is taken out by the output gear 18. When the rotational speed ratio between the input shaft 15 and the output gear 18 is changed, the pair of drive pistons 30 are displaced in opposite directions. In accordance with the displacement of the drive pistons 30, the pair of trunnions 6 are displaced in opposite directions, with the result that, for example, the lower (in FIG. 11) power roller 8 is displaced to the right in FIG. 11 and the upper power roller is displaced to the left in FIG. 11. As a result, directions of tangential forces acting on contact areas between peripheral surfaces 8a of the power rollers 8 and inner surfaces 2a, 4a of the input and output side discs 2, 4 are changed. As the directions of the forces are changed, the trunnions 6 are rocked around the pivot shafts 5 pivotally mounted on the support plates 20 in opposite directions. As a result, similar to the example shown in FIGS. 8 and 9, the contact areas between peripheral surfaces 8a of the power rollers 8 and inner surfaces 2a, 4a are changed, thereby changing the rotational speed ratio between the input shaft 15 and the output gear 18.
Incidentally, when the transmission of rotation is effected between the input shaft 15 and the output gear 18 in this way, due to the elastic deformation of the constructural parts, the power rollers 8 are displaced in the axial direction of the input shaft 15, and the displacement shafts 7 supporting the power rollers 8 are slightly rotated around the support shaft portions 22. As a result of such rotation, outer surfaces of the outer races 28 of the thrust ball bearings 26 and inner surfaces of the trunnions 6 are displaced relative to each other. Since there are the thrust needle bearings 27 between the outer surfaces and the inner surfaces, a force required for such relative displacement is small. Accordingly, the force for changing the inclination angles of the displacement shafts 7 in the above-mentioned manner becomes small.
Further, although not shown in FIGS. 10 and 11, lubricating oil (traction oil) is continuously supplied to contact areas (traction portions) between the peripheral surfaces 8a of the power rollers 8 and the inner surfaces 2a, 4a of the input and output side discs 2, 4 to form oil films on the contact areas. That is to say, in each contact area, for example, a contact elliptical zone having a dimension of about 4×10 mm is formed. For example, a great power exceeding 50 kw is transmitted, high surface pressure (or bearing) equal to or greater than 3.5 GPa act on central portions of such contact elliptical zones. Since heat generating amounts also becomes great in the traction portions to which such high surface pressure is applied, the traction oil must be supplied to the traction portions in order to cool the traction portions and maintain the oil films on the traction portions.
To this end, for example, lubricating devices as disclosed in Japanese Patent Application Laid-Open No. 4-29659 and Japanese Utility Model Application Laid-Open No. 2-47458 have been proposed. The lubricating device disclosed in the Japanese Utility Model Application Laid-Open No. 2-47458 serves to supply the traction oil to the traction portions through nozzle holes provided in the power rollers. On the other hand, in the lubricating device disclosed in the Japanese Patent Application Laid-Open No. 4-29659, in addition to the nozzle holes provided in the power rollers, nozzle holes for supplying the traction oil are also formed in a housing.
Further, Japanese Patent Application Laid-Open No. 11-210855 discloses a lubricating device as shown in FIGS. 12 and 13. In this conventional lubricating device, a lubricating post 33 is fixedly connected to, by a connecting screw 34, to a distal end of a support post 32 for supporting an intermediate portion of a support plate 20 for rocking movement and displacement movement in an axial direction (up-and-down direction in FIGS. 12 and 13) of pivot shafts 5. Among four nozzle holes, having downstream ends opened at four equidistant locations on the circumference of a hold-down flange 35, formed on a distal end of the lubricating post 34, downstream ends of two nozzle holes 36a shown in FIG. 13 are opened toward an inner surface 2a of an input side disc 2 and an inner surface 4a of an output side disc 4, respectively. On the other hand, downstream ends of two nozzle holes 36b shown in FIG. 12 are opened toward peripheral surfaces 8a of power rollers 8.
In operation of the toroidal type continuous variable transmission, traction oil is supplied to the above-mentioned four nozzle holes 36a, 36b through a lubricating oil supply groove 53 formed in an inner surface of a housing 37 by the action of an oil sending pump (not shown). The traction oil is injected from the downstream ends of four nozzle holes 36a, 36b. Among the traction oil injected from the nozzle holes 36a, 36b, the traction oil injected from two nozzle holes 36a shown in FIG. 13 is firstly adhered to the inner surfaces 2a, 4a of the input and output side discs 2, 4 and then is sent to the traction portions as contact areas between the inner surfaces 2a, 4a and the peripheral surfaces 8a of the power rollers 8. On the other hand, the traction oil injected from two nozzle holes 36b shown in FIG. 13 is firstly adhered to the peripheral surfaces 8a and then is sent to the traction portions.
In case of the toroidal type continuously variable transmission, adequate lubricating oil supplying must be performed for the following reason. That is to say, in the contact elliptical zones existing in the traction portions as the contact areas between the inner surfaces 2a, 4a of the input and output side discs 2, 4 and the peripheral surfaces 8a of the power rollers 8, spin as rotational slip component is generated during the operation of the toroidal type continuously variable transmission. Since the occurrence of such spin is inevitable and the spin is rotational slip component directing in perpendicular to the driving direction, the spin leads in power loss as it is. Such power loss is in the form of heat which increases temperatures of the input and output side discs 2, 4, power rollers 8 and traction oil existing in the traction portions. If the temperatures of the members 2, 4, 8 and the traction oil are increased, traction coefficient is reduced due to reduction in viscosity of the traction oil to generate slip, with the result that not only transmitting efficiency of the toroidal type continuously variable transmission is decreased but also damage of transmission such as seizure may occur if the temperatures are increased considerably.
In this way, in case of the toroidal type continuously variable transmission in which the traction oil existing on the traction portions transmits the power, it is important to suppress the increase in temperature at the traction portions in consideration of the heat generating amounts at the traction portions. However, the heat generating amounts at the traction portions are varied in dependence with not only the magnitude of power (load) passing through the toroidal type continuously variable transmission but also the transmission ratio and the number of revolutions. That is to say, since the magnitude of the above-mentioned spin is varied in dependence upon the transmission ratio and the number of revolutions, the heat generating amounts are also varied accordingly. Therefore, in order to prevent the reduction in transmitting efficiency and the damage due to the above-mentioned reason, it is preferable that the traction oil supplying condition is changed in accordance with the running condition of the toroidal type continuously variable transmission.
However, in case of the conventional toroidal type continuously variable transmissions including that shown in FIGS. 12 and 13, it is designed so that, during the running of the toroidal type continuously variable transmission, the traction oil is applied to given portions by predetermined amounts regardless of the running condition. On the other hand, the amount of the traction oil required for lubricating the traction portions as the contact areas between the inner surfaces 2a, 4a of the input and output side discs 2, 4 and the peripheral surfaces 8a of the power rollers 8 is varied with the running condition as mentioned above. More specifically, the greater the power to be transmitted from the input side disc 2 to the output side disc 4 the greater the required amount of the traction oil. Further, as apparent from FIGS. 8 and 9, the contact areas of the inner surfaces 2a, 4a of the input and output side discs 2, 4 contacted with the peripheral surfaces 8a of the power rollers 8a are changed in accordance with the transmission ratio between the discs 2 and 4.
In this regard, in the conventional designs, excessive traction oil was injected so that adequate traction oil can be supplied to the contact areas even when the power to be transmitted from the input side disc 2 to the output side disc 4 is great and even if the traction oil to be supplied to the inner surfaces 2a, 4a of the input and output side discs 2, 4 are deviated from the portions corresponding to the above-mentioned contact areas. In other words, the excessive traction oil was injected so that adequate traction oil can be supplied to the traction portions even under the most severe condition. Thus, not only power loss of the pump for supplying the traction oil under pressure becomes great, but also power loss due to agitating resistance of the excessive traction oil injected from the nozzles becomes great. As a result, the transmitting efficiency of the toroidal type continuously variable transmission is worsened. This is not preferable.
A toroidal type continuously variable transmission according to the present invention is devised in consideration of the above-mentioned circumstances.